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Why do people insist on downvoting in these types of questions. That's really in poor taste, I think. If you don't like something, just leave it alone.
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Philip ReganAug 31 '10 at 20:39

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Hmm.. the price probably depends on the Apple store (e.g. for me prices show in Euros) Which price should we note?
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Juan A. NavarroAug 31 '10 at 20:56

Records a few seconds of what you're currently listening to and then shows you information about this song. Shazam is quite old by now, but still an amazing piece of software that's always useful from time to time.

If you use 1Password on your Mac, the iOS app is quite handy. It can be linked to a Dropbox account therefore keeping data synchronized between your desktop and iOS device. There are regular and pro versions available for both iPhone and iPad.

For editing text on iPad & iPhone. PlainText is a simple text editor with a paper-like user interface. Unlike the default Notes app, PlainText allows you to create and organize your documents in folders and sync everything with Dropbox.com. Requires iOS 3.0+

After trying different note-taking apps like SimpleNote and Evernote, I discovered this beauty a few days ago and it immediately replaced the built-in Notes app for me, both on my iPhone and my iPad. It fit my needs perfectly, and is really simple & beautifully designed. YMMV, but it's free to try.

P.S. Elements is a feature-packed alternative with Markdown support and built-in email, but I'm not sure I need those features and it's $4.99.

SoudHound seems a lot faster than Shazam. Will start to try to match a song even before the full capture. It also identified songs that Shazam didn't. And SoundHound's free version allows unlimited matches, while Shazam allows 5 per month.

I bought into the angry birds hype, but quickly got over it. Realized it was just a trial and error game with a good physics engine, not exactly my forte. A great time waster nonetheless.
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xdumaineJan 31 '11 at 13:13

Cydia is a software application for iOS that is a graphical front end to APT and the dpkg package management system. It allows a user to browse and download applications for a jailbroken iPhone, iPod Touch or iPad.

WhatsApp Messenger is a smartphone messaging app which allows you to exchange messages with your friends and contacts without having to pay for SMS. WhatsApp Messenger is cross platform and available for iPhone, BlackBerry, Android and Nokia (beta) and yes, those phones can all message each other! To send and receive messages, WhatsApp utilizes your existing smartphone internet data plan: 3G/EDGE (or Wi-Fi when available)

In addition to messaging, iPhone, Android and BlackBerry WhatsApp Messenger users can send each other unlimited images, video and audio media messages.

This is awesome. There's an OS X app called Notational Velocity (that's also open source) that also syncs with Simplenote, and can be set to store notes in my Dropbox. This keeps my notes backed up locally, in the cloud, and in Simplenote's server as well as being editable across any platform. Such a great app/service.
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BrysonJun 3 '11 at 17:33

Now with iOS 4 + iPhone 4 (unlike with my unjailbroken iPhone 3G earlier) the experience is really good, as you get background play and ability to use normal iPod playback controls (e.g. the headphone remote). In other words, it's similar to using the built-in iPod app, except that you have approximately 10 million tracks available at your fingertips.

It’s a fast, beautiful and fun way to share your life with friends through a series of pictures. Snap a photo with your iPhone, choose a filter to transform the look and feel, send to Facebook, Twitter or Flickr – it’s all as easy as pie. It’s photo sharing, reinvented.

Trainyard

A great puzzle game with tons of levels. Kept me playing for days, and I've still been unable to beat a couple levels after a couple months of having the app. There is also a free version. Intuitive, fun, and brain exercising.

Soulver is by far the most useful calculator app in the App Store. It's a much easier and more powerful way to work with numbers over a normal calculator. Embed text with your calculations to make it easier to see the problem you are solving. You can easily go back and make a change earlier in the calculation and have everything updated, similar to a spreadsheet. You can use several lines and reference previous lines in your calculations allowing yourself to split up long equations or even reuse parts to see different results. These can all be saved on separate sheets so it's easy to go back and reference them later. You'll never go back to a normal calculator again.